[FairPlay] Safari screen mirroring cannot play back DRM protected video on iPhone, while Mac has no problem

I am a developer of FairPlay DRM. I would like to ask a problem to play back FairPlay protected video on the second screen.

I have a FairPlay DRM server that set the HDCP enforcement as "not required." The playback test of a FairPlay protected video was performed on Safari for Mac with a type-c-to-HDMI adapter, that connects to a HDCP-compatible monitor. The playback test was also performed on Safari for iPhone with Lightning-Digital-AV adapter (HDMI) connecting to the same monitor. The Mac case can play back the video well on both the main screen and the second out monitor. However, the iPhone case cannot play back the video for an error message of bitmovin player, "DRM: Content cannot be played back because the output is restricted on this machine." Does anyone have idea for this error or the different behavior between Safari for Mac and Safari for iPhone?

Follows attached application version:
Safari version on Mac: 13.1.2（14609.3.5.1.5）
Mac OS version: 10.14.6(18G103) MacBook Pro(13-inch, 2017)
iPhone X with iOS 13.5
Safari version on iPhone: 13
Lightning-digital-av-adapter: https://www.apple.com/tw/shop/product/MD826FE/A/lightning-%E6%95%B8%E4%BD%8D-av-%E8%BD%89%E6%8E%A5%E5%99%A8

Thank you,
Henry Lien